WO2019101909A1

WO2019101909A1 - Pet-detector for a combined pet/mri-scanner

Info

Publication number: WO2019101909A1
Application number: PCT/EP2018/082344
Authority: WO
Inventors: Pierre Gebhardt; David SCHUG; Thomas DEY; Nicolas GROSS-WEEGE; Volkmar Schulz; Bjoern Weissler
Original assignee: Rwth Aachen
Priority date: 2017-11-24
Filing date: 2018-11-23
Publication date: 2019-05-31
Also published as: DE102017221038A1; EP3713492A1

Abstract

The invention relates to a PET-detector (2) for a combined PET/MRI-scanner (1), said PET-detector (2) comprising a shielding (ES) against electromagnetic fields, such that electromagnetic fields generated by the MRI-scanner (3) are kept away from the PET-detector (2), and such that electromagnetic fields of the processing electronics of the PET-detector (2) are kept away from a receiver coil of the MRI-scanner (3), wherein the PET-detector (2) is suitable for use within the MRI-scanner (3), wherein the scanning unit (B) of the PET detector (2) is oriented substantially not in parallel with the main axis (A) of the MRI-scanner (3), wherein the shielding (ES) of the PET-detector (2) has at least one slot (S1; S2), which is perpendicular to the main axis of the MRI-scanner (A) at least in one projection, in order to prevent induced currents.

Description

PET detector for a combined PET / MRI scanner

The invention relates to a PET detector for a combined PET / MRI scanner.

Background of the invention

Positron emission tomography (PET) is a nuclear medicine imaging technique and is a variant of emission computed tomography. PET can be used to create sectional images of living organisms by visualizing the distribution of a radioactive substance called a tracer. As a result, biochemical and physiological functions can be mapped.

PET is based on the simultaneous detection of two gamma-ray photons that arise after the decay of a positron-emitting radionuclide (ß-i decay). In the interaction of a positron with an electron (annihilation) in the body, two high-energy photons are emitted in opposite directions. This radiation is also referred to as annihilation radiation.

The PET device typically includes many detectors for the photons annularly disposed about the patient. The principle of the PET study is to record coincidences between any two opposing detectors. From the temporal and spatial distribution of these registered decay events, the spatial distribution of the radioactive substance in the interior of the body is deduced and a series of sectional images is calculated.

Since the absorption of the photons depends only on the thickness of the irradiated tissue, but not on the origin of the photons, this also allows an accurate quantification of the distribution of the radioactive substance in the examination volume.

Much of the recent PET scanner is based on the fact that the two high-energy photons (gamma photons) are stopped in crystals in which a

Scintillation process generates optical photons. The crystals are therefore often referred to as scintillation crystals. The photons are then by optical Sensors recorded and converted into electrical impulses. Typically, photomultipliers are used as optical sensors. However, these are bulky and lead to significant restrictions in terms of size. If a high resolution is required, a large number of photomultipliers must be arranged, which leads to large apparatuses.

Magnetic Resonance Imaging (MRI) is an imaging technique that is used primarily in medical diagnostics to visualize the structure and function of tissues and organs in the body. It is physically based on the principles of nuclear magnetic resonance, in particular field gradient nuclear magnetic resonance, and is therefore also referred to as nuclear spin tomography. The abbreviation MRI also comes from the English term Magnetic Resonance Imaging and will be used in the following synonymous.

With the MRI one can produce sectional images of the human (or animal) body, which allow an evaluation of the organs and many morbid organ changes. It is based on very strong magnetic fields generated in a magnetic resonance tomography system as well as alternating magnetic fields in the high-frequency range, which resonantly excite certain atomic nuclei in the body, thereby inducing an electrical signal in a receiver circuit. An essential basis for the image contrast are different relaxation times of different types of tissue. In addition, the different content of hydrogen atoms in different tissues (eg muscle, bone) also contributes to the image contrast.

The method is based on the fact that the atomic nuclei in the examined tissue are selectively excited synchronously to a certain movement by a combination of static and high-frequency magnetic fields and then deliver a measurable signal in the form of an alternating voltage until the movement has subsided. This movement is called Larmorpräzession and is mechanically analogous to a toy gyroscope observed when its axis of rotation is not vertical, but performs a precession around the vertical. Both for the excitation and for the observation of the signal a resonance condition is to be fulfilled, by means of which it is possible by means of inhomogeneous static magnetic fields to determine the location of the precessing nuclei.

Some atomic nuclei (such as the hydrogen nuclei) in the molecules of the tissue to be examined have an intrinsic angular momentum (nuclear spin) and are therefore magnetic. These nuclei generate a small longitudinal magnetization in the direction of the static field (paramagnetism) after application of a strong static magnetic field. Through a short-term applied additional high-frequency alternating field in the radio frequency range This magnetization can be deflected (tilted) from the direction of the static field, ie transform partially or completely (saturation) into a transverse magnetization. The transverse magnetization immediately starts to precess around the field direction of the static magnetic field, ie the direction of magnetization rotates (see figure on precession). This precession movement of tissue magnetization, like the rotation of the magnet in the dynamo in a coil (receiver circuit), induces an electrical voltage and can thus be detected. Their amplitude is proportional to the transverse magnetization.

After switching off the high-frequency alternating field, the transverse magnetization decreases (again), so the spins align themselves again parallel to the static magnetic field. For this relaxation they need a characteristic cooldown. This depends on the chemical compound and the molecular environment in which the precessing hydrogen nucleus is located. Therefore, the different types of tissue characteristically differ in their signal, resulting in different signal strengths (brightnesses) in the resulting image.

A relatively recent development is the combination of PET and MRI in a single device as a new diagnostic method for clinical use. They allow combined PET / MRI examinations. Essentially, there are two approaches available.

In an integrated approach, the PET detector is mounted behind a shield so that the RF coils of the MRI scanner essentially represent the inner part. However, this structure is very complex and therefore costly. In addition, this structure requires a large area and therefore can not be realized everywhere. With simultaneous PET-MRI systems, the photomultipliers normally used in PET scanners can not be used because of the magnetic field necessary for MRI imaging.

In a separate approach, e.g. only the patient bed is divided and the examination by means of the scanner is carried out in chronological order with respect to the area to be examined. Typically, the distance between each scanner is 1 meter or more. Frequently, the temporally and spatially separated examination results are then reunited by software. These previously known devices have a common axis.

Metal on or in the body can cause side effects and image disorders in MRI. This means that even metals that are part of a PET scanner, for example, can interfere. Vice versa Of course, parts of the PET scanner can also be damaged by induced currents.

Another problem is that for certain tumors, positioning closer to the potential tumor could lead to better resolution in terms of location. However, if a PET scanner is constructed analogously to a MRI scanner with a large opening, so that a patient could be pushed through the opening, the spatial resolution and / or the sensitivity suffers, since the solid coverable by PET detectors solid angle with increasing distance becomes smaller.

Although it would be possible to use new semiconductor-based sensors for the PET detectors and thus allow an arrangement within an MRI scanner, but then the PET detector electronics must be shielded electromagnetically, because in the excitation phase by an MRI scanner partly very strong alternating fields generated, which can lead to a disturbance of the electronics, in particular of amplifiers, to destruction. In addition, during the decay phase - the actual scanning phase - the MRI scanner is very sensitive to electromagnetic interference, which can arise from the electronics of the PET scanner.

Based on this situation, it is an object of the invention to provide a PET detector for a combined PET / MRI scanner, which makes it possible to avoid one or more disadvantages of the prior art.

The problem is solved by a PET detector for a combined PET / MRI scanner. The PET detector has a shield against electromagnetic fields so that electromagnetic fields generated by the MRI scanner are kept away from the PET detector, and so that electromagnetic fields from the processing electronics of the PET detector are received by a receiving coil of the MRI scanner. Scanner is kept away. The PET detector is suitable for use within the MRI scanner, wherein the scanning direction of the PET detector is substantially not aligned parallel to the main axis of the MRI scanner. The shield of the PET-PET detector has at least one slot which is at least in a projection perpendicular to the main axis of the MRI scanner in order to avoid induced currents.

In one embodiment of the invention, the shield has a fiber reinforced material. According to a further embodiment of the invention, the shield has an electrically conductive polymer.

In yet another embodiment of the invention, the shield comprises soot.

According to yet another embodiment of the invention, the shield has at least two slots perpendicular to the main axis of the MRI scanner to avoid induced currents.

In a further embodiment of the invention, the PET detector is openable with respect to the at least one slot.

According to a further embodiment of the invention, at least one slot is arranged sagittally, parasagittally or transversely with respect to a patient to be examined.

According to one embodiment of the invention, a PET detector according to the invention can be used for imaging a female breast or scrotum.

Further advantageous embodiments are in particular subject of the dependent claims, the description and the figures.

The invention will be explained in more detail with reference to the figures. In these shows:

1 shows an exemplary arrangement of a PET scanner according to embodiments of the invention in connection with an MRI scanner,

2 shows a detail of an embodiment of a PET scanner according to the invention,

3 shows a detail of a further embodiment of a PET scanner according to the invention,

4 shows a further detail of an embodiment of a PET scanner according to the invention,

5 shows a further detail of a further embodiment of a PET scanner according to the invention,

6 shows a further detail of an embodiment of a PET scanner according to the invention in a first state in a perspective view,

Fig. 7 shows the detail of Fig. 6 of a PET scanner according to the invention in a second state in a plan view, and

Fig. 8 shows a detail to illustrate the term PET scanner. Detailed description

Hereinafter, the invention will be illustrated in more detail with reference to the figure. It should be noted that various aspects are described, which can be used individually or in combination. That Any aspect may be used with different embodiments of the invention, unless explicitly illustrated as a mere alternative.

Furthermore, in the following, for the sake of simplicity, usually only one entity will be referred to. Unless explicitly stated, however, the invention may also have several of the entities concerned. As such, the use of the words "a," "an" and "an" is to be understood merely as an indication that at least one entity is used in a simple embodiment.

Parts of a PET detector 2 according to the invention for a combined PET / MRI scanner 1 are shown in the figures.

The PET detector 2 has a plurality of individual detectors D _; ... D _NM , which are arranged about an axis B. Such a field of individual detectors D _; ... D _NM is "unwound" in FIG.

The detectors Du,... D _NM are preferably produced on the basis of semiconductors, for example based on silicon (optionally with (avalanche effect) amplification). Such semiconductor detectors allow a slimmer design so that the detectors can be provided in higher density and / or smaller space. As a result, the performance, in particular the spatial resolution, can be greatly increased. In particular, semiconductor detectors can also be used within MRI scanners.

An associated electronics for evaluation can be arranged directly at each individual detector or organized in groups. In this case, an emission is detected by the PET scanner 2 in the usual way by detecting two photons by opposing detectors.

The PET detector 2 also has a shield ES against electromagnetic fields, so that electromagnetic fields generated by the MRI scanner 3, of the PET detector 2, but in particular of the sensitive processing / amplifier / Auswertelogik of PET Detector, is kept away. The shield ES also has the task of keeping electromagnetic fields from the processing electronics of the PET detector 2 from a receiving coil of the MRI scanner 3 That is, the shielding protects on the one hand the PET detector 2, on the other hand also the MRI scanner 3.

The PET detector 2 is suitable for use within the MRI scanner 3. In this case, the scanning direction / axis B of the PET detector 2 is substantially not aligned parallel to the main axis A of the MRI scanner 3. The main axis A of the MRI scanner 3 results essentially as the axis of the transmitting coil TX of the MRI scanner 3 or of the receiving coil RX of the MRI scanner 3.

In order to avoid that eddy currents occur in the arrangement of the PET-PET detector 2, which could disturb the PET detector 2, which could also lead to a strong warming and thus burns on the patient, and which would also be suitable, the measurement result of the MRI scanner 3, the shield ES of the PET-PET detector 2 has at least one slit S ^ S ₂ , which is at least in a projection perpendicular to the main axis of the MRI scanner A in order to avoid induced currents.

Although the PET detector 2 has been described above in terms of integration with an MRI scanner 3, the PET detector 2 is not limited thereto and may be combined with other diagnostic imaging devices.

The above arrangement makes it possible to provide a PET scan of a region to be examined as well as an MRI scan of a region to be examined in high resolution on the one hand.

For example, the PET detector 2 may be incorporated with an MRI scanner 3 in a common PET / MRI scan 1. For example, two PET detectors 2, 2 'may be provided below an opening of a patient bed L for the detection of breast cancer. The patient is positioned on the patient couch L such that each breast is inserted into one of the PET detectors 2, 2 '. Thus, during an MRI scan, each breast can also be scanned by a PET detector 2, 2 '. In this arrangement, it is also possible, in particular, to scan lymph nodes adjacent thereto, for example axillary lymph nodes, by means of the MRI scan. For example, a PET detector 2 may be provided below another opening of a patient bed L (not shown) for the detection of testicular cancer. The patient is positioned on the patient couch L so that the testicle is inserted into the PET detector 2. Thus, during an MRI scan, the testes can also be scanned by a PET detector 2. In this arrangement, it is in particular also possible by means of the MRI scan to scan lymph nodes adjacent thereto, for example retroperitoneal lymph nodes. That is, the PET detector 2 or the PET detectors 2, 2 'can be suitably arranged in the narrow space under the patient bed L. For breast examinations, for example, it should be noted that the space around the breastbone (sternum) is small, so that the PET detectors 2, 2 'must not exceed certain sizes in a juxtaposed arrangement. This is not possible with conventional PET detectors , On the other hand, the invention allows the juxtaposition, as indicated in Figure 1.

It should be noted that although in principle it would be possible to provide a combined PET / MRI scanner only for a particular tissue. However, due to the spatial limitations, it would hardly be possible to reasonably integrate this. Moreover, while it would then be possible to capture the primarily interesting study area, e.g. Information regarding adjacent lymph nodes can no longer be captured, which would severely limit the diagnostic benefit.

By means of the invention, however, a PET detector 2, 2 'which is transparent for the MRI scanner 3 is now made available.

In principle, it would be possible to construct the PET detector 2, 2 ', for example, from thin, elongated and galvanically separated detectors Du, ... D _NM . Then the high-frequency alternating field provided by the MRI scanner 3 could pass through the gaps. However, this would lead to the design of the PET detectors 2, 2 'would be very expensive, since then each individual detector Du, ... D _{NM would} require its own power supply, data processing, data forwarding. Furthermore, a complex synchronization would be needed to allow a meaningful evaluation. All this would lead to room requirements increasing, making integrated placement almost impossible.

In the arrangement of Figure 1, in which the transmitting coil TX and the receiving coil RX are shown (while, for example, a static magnet and a gradient field coil are not shown), one can decompose a rotating magnetic field into two linear field components, wherein one of the field components F _B in Direction of the axis B of the PET detector 2, 2 'is coaxially oriented and a field component F _A , which is perpendicular thereto, for example, in the main scanning direction A. In this case, the vertical field component would be at least partially by the PET detector 2, 2' in Dependent on the screen ES shielded. However, the coaxial field component F _B would generate an eddy current in the annular shielded arrangement, producing counteractive fields that counteract the corresponding field component such that the field component would drop to an unusable field strength. However, through the slit S ₂ S ₂ , the eddy current flow in the ring-like configuration of the PET detectors 2, 2 'is interrupted. Thus, the PET detector 2, 2 'but at least for this field portion (semi-) transparent, so that the signal of the MRI scanner 3 can be sensibly utilized in terms of metrology and diagnostics. It should be noted that the receiving coil RX can alternatively or additionally also be arranged differently, for example closer to the area to be examined. For this purpose, for example, reception coils can be arranged in the immediate vicinity of the area to be examined within the transmission coil TX.

In this arrangement, the processing / amplification / evaluation logic of the PET detector 2, 2 'may be organized in a tree-like structure.

In one embodiment of the invention, the shield ES comprises a fiber-reinforced material, for example a material with carbon fibers, glass fibers, carbon nanotubes. Furthermore, the shield ES may comprise an electrically conductive polymer. The electrically conductive polymer may be intrinsically conductive, e.g. based on polyaniline, and / or by adding fillers or excipients, e.g. Nickel or carbon black, give the shield ES electrical conductive properties.

In one embodiment, which is shown in FIG. 2, it is shown that the screen ES of the PET detector can also have more than one slot S1. In the example of FIG. 2, the shield ES has two slits S ₂ S ₂ perpendicular to the main axis A of the MRI scanner 3 in order to avoid induced currents.

It should be noted that the manner of the slit Si / slits S _{1 s} S _{2 can} also be selected such that, at least in one projection of the slit, it is perpendicular to the main axis A of the MRI scanner 3. That is, other slot shapes, such as shown in Figure 5, or even more complicated slot profiles, such as staircase-like configurations, are possible by the invention and still allow the provision of electrical properties.

In addition, as shown in FIGS. 6 and 7, an opening of the PET detector 2, 2 'can be made possible through the slots Si, S _{2 in} order, for example, to easily insert a tissue to be examined into the opened PET detector 2, 2' (FIG 7) to introduce. Subsequently, the PET detector 2, 2 'can be "closed", eg by moving the two partial halves of the PET detector 2, 2' relative to one another with respect to a hinge G which is arranged at the slot S2 (FIG. 6). , Of course, one of the partial halves of the PET detector 2, 2 'be fixed, for example by attachment to the patient bed L.

In this case, the slot (s ₎ S ₂ S ₂ may be arranged substantially sagittally, parasagittally or transversely with respect to a patient to be examined.

Claims

claims

1. PET detector (2) for a combined PET / MRI scanner (1), comprising the PET detector (2)

Electromagnetic field shielding (ES) such that electromagnetic fields generated by the MRI scanner (3) are kept away from the PET detector (2) and electromagnetic fields from processing electronics of the PET detector (2) is kept away from a receiver coil of the MRI scanner (3),

Wherein the PET detector (2) is suitable for use within the MRI scanner (3),

Wherein the scanning direction (B) of the PET detector (2) is substantially not aligned parallel to the main axis (A) of the MRI scanner (3),

Wherein the shield (ES) of the PET-PET detector (2) has at least one slot (Si; S ₂ ) which is at least in a projection perpendicular to the main axis of the MRI scanner (A) to avoid induced currents.

2. PET detector (2) according to claim 1, characterized in that the shield (ES) comprises a fiber-reinforced material.

3. PET detector (2) according to claim 1 or 2, characterized in that the shield (ES) comprises an electrically conductive polymer.

4. PET detector (2) according to one of the preceding claims, characterized in that the shield (ES) has soot.

5. PET detector (2) according to one of the preceding claims, characterized in that the shield (ES) at least two slots (S ^ S ₂ ) perpendicular to the main axis (A) of the MRI scanner to avoid induced currents.

6. PET detector (2) according to one of the preceding claims, characterized in that the PET detector (2) with respect to the at least one slot (Si, S ₂ ) can be opened.

7. PET detector according to one of the preceding claims, characterized in that the at least one slot (Si; S ₂ ) is arranged sagittal, parasagittal or transverse with respect to a patient to be examined.

8. Use of a PET detector (2) according to one of the preceding claims for imaging a female breast.

9. Use of a PET detector (2) according to any one of the preceding claims 1 to 7 for imaging a scrotum.